"Mommy, go away!"

I'd say continue what you're doing. My 2 year old like to tell us "stop it" which is also irritating. We just tell him we are the boss and he can't tell us what to do. Does he still don't? Sure. But they're 2. Takes a long time to crack a stubborn 2 year old lol

oh yeah. my dd is like that. she says stupid. but only because she is repeating from us. i never realize how much we say things that we are just aware of. anyways, i would continue what you are doing.  I usually redirect and explain calmly why we do not say that word or in your case a phase.  if anything 2 yr olds will move on to other things eventually. mine is 3. trust me its worse. lol enjoy your 2s.

my dd has picked up "go away" "stop it" etc. but she points her finger in my face which drives me nuts.  her latest is "stop saying that".  she's gotten them all from big brother yelling at her.  i just tell her "not nice" and correct her just as you are doing.  they are young so we just have to be patient and lead by example.

He is starting to exert a little independence.  He wants time alone to figure things out.  This is actually very healthy behavior- do you want a child who clings to you constantly and refuses to do anything alone?  What you need to do is establish the proper way to ask for things he wants.  If he wants to be alone, he needs to ask politely to have some personal time.  It's okay to want to be alone.  It's not okay to be rude.

My daughter (who is almost 3) has been doing this too. Or she says, "Mommy you can't come in my room." I just tell her that's not a nice thing to say and it hurts my feelings, and then I walk away. If she says it again I ignore her. 

Continue to ignore and redirect at this point.  DO you knwo why he's saying it other than the "novelty" and "you've said it all this time"?

Whenever I want my children to stop saying things, typically ignoring works the best.